TDMA & CDMA Technologies

What is TDMA?

Time Division Multiple Access (TDMA) : a digital wireless telephony transmission technique. TDMA allocates each user a different time slot on a given frequency. TDMA divides each cellular channel into three time slots in order to increase the amount of data that can be carried.

TDMA technology was more popular in Europe, Japan and Asian countries, where as CDMA is widely used in North and South America. But now a days both techologies are very popular through out of the world.

Advantages of TDMA:

TDMA can easily adapt to transmission of data as well as voice communication.

TDMA has an ability to carry 64 kbps to 120 Mbps of data rates.

TDMA allows the operator to do services like fax, voice band data, and SMS as well as bandwidth-intensive application such as multimedia and video conferencing.

Since TDMA technology separates users according to time, it ensures that there will be no interference from simultaneous transmissions.

TDMA provides users with an extended battery life, since it transmits only portion of the time during conversations.

TDMA is the most cost effective technology to convert an analog system to digital.

Disadvantages of TDMA

Disadvantage using TDMA technology is that the users has a predefined time slot. When moving from one cell site to other, if all the time slots in this cell are full the user might be disconnected.

Another problem in TDMA is that it is subjected to multipath distortion. To overcome this distortion, a time limit can be used on the system. Once the time limit is expired the signal is ignored.

What is CDMA ?

Code Division Multiple Access (CDMA: a digital wireless technology that uses spread-spectrum techniques. CDMA does not assign a specific frequency to each user. Instead, every channel uses the full available spectrum. Individual conversations are encoded with a pseudo-random digital sequence. CDMA consistently provides better capacity for voice and data communications than other commercial mobile technologies, allowing more subscribers to connect at any given time, and it is the common platform on which 3G technologies are built.

Advantages of CDMA

One of the main advantages of CDMA is that dropouts occur only when the phone is at least twice as far from the base station. Thus, it is used in the rural areas where GSM cannot cover.

Another advantage is its capacity; it has a very high spectral capacity that it can accommodate more users per MHz of bandwidth.

Disadvantages of CDMA

Channel pollution, where signals from too many cell sites are present in the subscriber. s phone but none of them is dominant. When this situation arises, the quality of the audio degrades.

When compared to GSM is the lack of international roaming capabilities.

The ability to upgrade or change to another handset is not easy with this technology because the network service information for the phone is put in the actual phone unlike GSM which uses SIM card for this.

Limited variety of the handset, because at present the major mobile companies use GSM technology.